I don't know much about SPG admittedly, but I know a lot about wordpress websites and specifically how to optimize them.
There is virtually no performance difference with the core platform. Performance is only sacrificed by unnecessary plugins for one function, bloated themes with built-in page builders, and poor image/code optimization by the designer/developer. What you save in milliseconds by building a site statically is instantly wasted by longer development times.
In terms of security, every site is at risk. Wordpress, when managed properly, is just as safe as a static website. With plugins like WordFence you could even argue it's safer because I can easily blacklist suspicious IP's.
With all of that being said, if I ever want to do things a specific way I have simply just said this is the best way. I'm the developer, I'm the one building it, my clients pay me for my expertise and knowledge. It's literally that simple.
My first boss said it best, "I use the language and platform that makes me the most money."
Yes, and I wish more developers took off their kool-aid glasses before making technology decisions. Ongoing support, ecosystem and availability of talent are major, major factors.
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